Delegates are considering scaling back the assault weapons ban in Gov. Martin O'Malley's gun bill to keep legal the sale of guns used recent mass shootings in Newtown, Conn. and Aurora, Colo.

O'Malley blasted an email to supporters Thursday morning, calling on them to contact lawmakers to keep the assault weapons ban intact.

"Military-style assault weapons belong on the battlefield, NOT on the streets of our cities and towns," the email said. "We need you to ACT NOW."

Lt. Gov. Anthony Brown, flanked by police chiefs, held a press conference Thursday morning to urge lawmakers to pass the "common-sense, balanced approach" that has already been approved by the Senate.

Members of the House Judiciary Committee have been considering how to scale back the ban, which is modeled on the federal ban that expired in 2004. Delegates are considering taking the AR-15 and the Bushmaster semi-automatic rifle off the list of banned weapons, members said, as well as taking off some of the features that would ban other guns.

Lawmakers said they questioned whether banning the sale of the those guns, popular among gun-owners, would substantially cut down on gun violence to justify banning them.

The push-back against the full ban comes as the proposed federal assault weapons ban appears to have died in the U.S. Senate.